To meet the demand for wireless data traffic, which has increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long-term evolution (LTE) system’.
It is considered that the 5G communication system will be implemented in millimeter wave (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To reduce propagation loss of radio waves and increase a transmission distance, a beam forming technique, a massive multiple-input multiple-output (MIMO) technique, a full dimensional MIMO (FD-MIMO) technique, an array antenna technique, an analog beam forming technique, and a large scale antenna technique are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a device-to-device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, and the like.
In the 5G system, a hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and a sliding window superposition coding (SWSC) as an advanced coding modulation (ACM) scheme, and a filter bank multi carrier (FBMC) scheme, a non-orthogonal multiple Access (NOMA) scheme, and a sparse code multiple access (SCMA) scheme as an advanced access technology have been developed.
A communication system has been developed to support a higher data rate for satisfying a continuously increased wireless data traffic demand. For example, a communication system has been developed to enhance spectral efficiency and increase channel capacity based on various schemes such as an orthogonal frequency division multiplexing (OFDM) scheme, a multiple input multiple output (MIMO) scheme, and/or the like for increasing a data rate.
Specially, the MIMO scheme is a scheme in which a signal transmitting apparatus, e.g., a base station increases system capacity using a plurality of antennas. In the early days of the MIMO scheme, a study for a scheme of increasing capacity by increasing the number of antennas used in each of a signal transmitting apparatus and a signal receiving apparatus, e.g., a station has been mainly progressed.
However, considering actual implementation, the MIMO scheme has been developed to increase the number of antennas used in a signal transmitting apparatus, e.g., a base station which is relatively easy to actually implement in terms of a size and complexity than a signal receiving apparatus, e.g., a station which is relatively difficult for antenna expansion and complex computation due to a size and available power limitation.
In a 3rd generation partnership project (3GPP) Release 10 standard also referred to as long-term evolution-advanced (LTE-A), a transmitting scheme for a base station supporting up to 8 antennas has been developed. Recently, in the LTE-A, study for an FD-MIMO scheme in which a base station supports up to 64 antennas has been actively progressed.
Meanwhile, in a uniform linear array (ULA) antenna where a relatively large number of antennas are arranged only in a horizontal direction or the relatively large number antennas are arranged only in a vertical direction, a space which element antennas included in the ULA antenna occupy is very large, so it is practically impossible to implement the ULA antenna. For example, in a case that 64 element antennas are arranged at a λ/2 distance only in a horizontal direction or the 64 element antennas are arranged at the λ/2 distance only in a vertical direction, a total length which the 64 element antennas occupy is about 5 m. So, considering a base station space in communication systems which have been proposed up to now, it is impossible to practically implement the UPA antenna.
So, a uniform planar array (UPA) antennas with a structure different from this ULA antenna has been considered in the communication system supporting the FD-MIMO scheme. Here, the UPA antenna has a form in which a plurality of element antennas are arranged in a two-dimensional space considering all of a horizontal direction and a vertical direction. The UPA antenna enables to solve spatial limitation problem in a base station which has been proposed up to now and to practically implement an FD-MIMO scheme which is based on a plurality of antennas.
It is possible to support an FD-MIMO scheme which may use a relatively large number of antennas by using the UPA antenna, so a base station may support a larger number of antennas than before. So, the base station has been tried to equip a large number of antennas and to increase system capacity of a wireless communication system using these antennas.
For increasing system capacity, channel information between a signal transmitting apparatus, e.g., a base station and a signal receiving apparatus, e.g., a station is required. In a case of a communication system supporting a frequency division duplexing (FDD) scheme, a signal receiving apparatus estimates channel information using a reference signal (RS) received through a downlink signal and feeds back the estimated channel information to a signal transmitting apparatus through a uplink in order to provide channel information required in the signal transmitting apparatus.
Further, in a communication system supporting an LTE-Advanced scheme, a signal receiving apparatus estimates channel information using a channel state information-reference signal (CSI-RS) received through a downlink signal and feeds back the estimated channel information to a signal transmitting apparatus through a uplink in order to provide channel information required in the signal transmitting apparatus. For exact channel estimation, a CSI-RS is designed so that each antenna has an orthogonal characteristic, e.g., a time dimension, a frequency dimension, and a code dimension. Due to this orthogonal characteristic, if the number of antennas is increased, resources used for CSI-RS transmission are also increased.
This characteristic of a CSI-RS, i.e., a characteristic that resources used for CSI-RS transmission are increased according to increase of the number of antennas becomes more serious in a communication system supporting an FD-MIMO scheme which supports a relatively large number of antennas.
So, there is a need for a reference signal transmitting/receiving scheme in which it is possible for a signal receiving apparatus to exactly estimate channel information and to decrease the number of resources used for transmitting a reference signal in the communication system supporting the FD-MIMO scheme.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.